A method for setting relay protection values ​​in distribution network considering the impact of voltage sag

Abstract

The present invention discloses a method for setting relay protection constants of a distribution network considering the influence of voltage sag, including: obtaining the voltage sag amplitude at the access point of sensitive loads in the distribution network; judging whether a multi-level sag occurs; determining the line protection action time according to a comprehensive prediction model; and realizing the setting of the relay protection time of the distribution network according to the voltage sag amplitude, the protection action time, and the ITIC curve. The present invention uses the standard ITIC curve of the bearing capacity of sensitive equipment as a reference value, combines the relay protection action time, and aims to improve the voltage sag bearing capacity of sensitive loads, realizes the setting calculation of relay protection constants for the entire network with potential safety hazards, improves the speed of protection action when a fault occurs, shortens the duration of voltage sag, greatly reduces the impact of voltage sag on sensitive equipment, realizes low-cost mitigation of voltage sag, and effectively reduces the operation risk of the power grid.

Description

Technical Field

[0001] The invention relates to a distribution network relay protection setting value setting method considering the influence of voltage sag, and belongs to the technical field of distribution network relay protection. Background Art

[0002] The relay protection system is a safety net for the power system. Its function is to monitor abnormal conditions in the power system and quickly cut off the fault section when a fault occurs to prevent the fault from expanding and causing serious consequences. If the relay protection system cannot work in a timely and accurate manner, it may cause the power system fault to expand, causing serious personal injury and property loss. In the prior art, the relay protection setting values ​​of the distribution network are usually only manually set based on actual test data and the experience of engineers, and the accuracy of the relay protection setting values ​​is poor. In addition, in the process of determining the relay protection setting parameters, factors such as system reliability, safety, and economy also need to be considered. In addition, with the access of a large number of new energy sources to the power system, the distribution network structure has become diverse and complex, and the setting of relay protection settings has become increasingly difficult.

[0003] In order to better ensure its reliability, the relay protection setting process of the distribution network often chooses to sacrifice its speed. However, the relay protection does not take effect, resulting in the continued existence of the fault, which will cause the voltage of each node in the system to change, that is, voltage sag. The voltage sag will cause sensitive equipment to fail to work properly, affect product quality, and even cause shutdown and production, resulting in serious economic losses. The voltage sag process ends after the relay protection action removes the fault, so deliberately extending the protection action time will increase the impact of the voltage sag on sensitive equipment in the system.

[0004] In summary, the existing distribution network relay protection setting process cannot meet the user's requirements for safe and reliable power supply, and the relay protection devices installed on the transmission lines will significantly change the voltage sag index value. Therefore, it is necessary to consider the impact of voltage sag in the process of setting the distribution network relay protection settings. Summary of the invention

[0005] The present invention provides a method for setting relay protection values ​​of a distribution network considering the influence of voltage sag. The protection action characteristics are combined with sensitivity curves for analysis. The purpose is to focus the influence of relay protection on the voltage sag phenomenon, realize the setting of relay protection values ​​of the distribution network considering the influence of voltage sag, and solve the shortcomings of low setting efficiency, waste of manpower and material resources caused by empirical methods.

[0006] The technical solution of the present invention is:

[0007] According to one aspect of the present invention, a method for setting relay protection settings of a distribution network considering the influence of voltage sag is provided, comprising:

[0008] Step 1, obtaining the voltage sag amplitude at the sensitive load access point of the distribution network;

[0009] Step 2, determining whether a multi-level sag occurs: if a multi-level sag occurs, recalculating the voltage sag amplitude at the sensitive load access point;

[0010] Step 3: Determine the line protection action time based on the comprehensive prediction model;

[0011] Step 4: According to the voltage sag amplitude, protection action time, and ITIC curve, the distribution network relay protection time setting is realized.

[0012] The step 2 is specifically:

[0013] If multi-level voltage sag occurs, the distribution network topology will change, and the impedance matrix formed by the original distribution network structure needs to be corrected to recalculate the voltage sag amplitude, otherwise it will remain unchanged.

[0014] The comprehensive prediction model specifically comprises: using an exponential smoothing analysis model and a regression analysis model to generate respective prediction value data for the historical voltage sag duration series data of the distribution network, and performing weighted synthesis on the prediction values ​​to obtain final prediction data.

[0015] The voltage sag amplitude, protection action time, and ITIC curve are combined to realize the setting of the relay protection time of the distribution network, specifically:

[0016] If the voltage sag amplitude U sag And protection action time t sag When located in the equipment damage area, the tolerance of sensitive load equipment is classified as Class A. sag In this case, the first maximum time point in the equipment non-destructive zone is used as the new setting protection time constant;

[0017] If the voltage sag amplitude U sag And protection action time t sag When it is in the tolerance zone, the equipment tolerance is classified as Class AA. sag In this case, the second maximum time point in the equipment non-destructive zone is used as the new setting protection time constant;

[0018] If the voltage sag amplitude U sag And protection action time t sag When located in the equipment non-damage zone, the equipment's bearing capacity is classified as AAA and the initial set value is used.

[0019] The first maximum time point in the damage-free zone of the equipment is taken as follows: the voltage sag amplitude U sagThe sag time at the intersection of the voltage and the equipment damage area is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the first maximum time point<the voltage sag amplitude U between the equipment intact area and the equipment damaged area sag The sag time at the intersection of .

[0020] The second maximum time point in the equipment lossless zone is taken as follows: the voltage sag amplitude U sag The sag time at the intersection of the equipment non-destructive zone and the equipment tolerance zone is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the second maximum time point<the voltage sag amplitude U between the equipment non-destructive zone and the equipment tolerance zone sag The sag time at the intersection of .

[0021] According to another aspect of the present invention, there is provided a distribution network relay protection setting system considering the influence of voltage sag, comprising:

[0022] An acquisition module is used to obtain the voltage sag amplitude at the access point of sensitive loads in the distribution network;

[0023] A judgment module is used to judge whether a multi-level sag occurs: if a multi-level sag occurs, the voltage sag amplitude of the sensitive load access point is recalculated;

[0024] A determination module, used to determine the line protection action time according to the comprehensive prediction model;

[0025] The execution module is used to set the relay protection time setting value of the distribution network according to the voltage sag amplitude, protection action time and ITIC curve.

[0026] The beneficial effects of the present invention are as follows: the present invention uses the standard ITIC curve of the bearing capacity of sensitive equipment as a reference value, combines the relay protection action time, aims to improve the voltage sag bearing capacity of sensitive loads, realizes the setting calculation of relay protection constants with potential safety hazards in the entire network, improves the quickness of protection action when a fault occurs, shortens the duration of voltage sag, greatly reduces the impact of voltage sag on sensitive equipment, and realizes low-cost voltage sag mitigation; at the same time, it avoids the problem that the setting calculation results of traditional setting calculation results may not meet the coordination requirements with the upper-level line protection, which is conducive to the staff to make setting optimization strategies in time and effectively reduce the operation risks of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a method for setting relay protection settings in a distribution network taking into account the impact of voltage sag;

[0028] Figure 2It is a voltage sag amplitude evaluation model system in the present invention;

[0029] Figure 3 It is a schematic diagram of setting protection time when voltage drops temporarily in the damaged area of ​​equipment using ITIC curve in the present invention;

[0030] Figure 4 It is a schematic diagram of setting protection time under voltage sag in the tolerance zone of ITIC curve in the present invention;

[0031] The numbers in the figure are: p is the sensitive load access node, ij is a line in the system, f is the short-circuit fault point on line ij, and l is the ratio of the length of the fault point f to the node i to the total line ij. DETAILED DESCRIPTION

[0032] The invention will be further described below in conjunction with the accompanying drawings and embodiments, but the content of the invention is not limited to the scope of the embodiments.

[0033] Example 1: Figure 1-4 As shown, according to one aspect of an embodiment of the present invention, a method for setting a relay protection setting value of a distribution network considering the influence of voltage sag is provided, comprising:

[0034] Step 1, obtaining the voltage sag amplitude at the sensitive load access point of the distribution network; when a short circuit fault occurs, the network structure of the power system of the distribution network changes, the voltage amplitude of the sensitive load access node changes, and the voltage sag amplitude at the sensitive load access point is determined;

[0035] Step 2, determining whether a multi-level sag occurs: if a multi-level sag occurs, recalculating the voltage sag amplitude at the sensitive load access point;

[0036] Step 3: Determine the line protection action time based on the comprehensive prediction model;

[0037] Step 4: According to the voltage sag amplitude, protection action time, and ITIC curve, the distribution network relay protection time setting is realized.

[0038] In step 1, an example is given as follows:

[0039] When calculating the voltage sag amplitude, this method calculates the node voltage sag amplitude when the system has symmetrical faults and asymmetrical faults based on the node impedance matrix. When an asymmetrical fault occurs, Figure 2 In the voltage sag amplitude assessment model system, assume that busbar p is the sensitive load access node, and a short circuit fault occurs at point f on a line ij in the system. l is the ratio of the length of the fault point f to the node i to the total line ij. The voltage sag amplitude V of busbar p is b for:

[0040]

[0041] in, n=0,1,2, indicating zero sequence, positive sequence and negative sequence; and is the voltage amplitude of busbar p and point f before the fault at point f; is the mutual impedance between busbar b and fault point f; and is the mutual impedance between nodes; is the short-circuit current at the fault point f; and is the self-impedance; is the mutual impedance between lines ij.

[0042] The calculation formula for the voltage sag amplitude when a three-phase symmetrical short circuit occurs at the terminal line protection outlet is as follows:

[0043]

[0044] and is the voltage of the target bus P and the fault point f before the fault.

[0045] Furthermore, the step 2 is specifically:

[0046] If a multi-level voltage sag occurs, the distribution network topology will change, and the impedance matrix formed by the original distribution network structure needs to be corrected to recalculate the voltage sag amplitude, otherwise it will remain unchanged (i.e., determine the voltage sag amplitude at the sensitive load access point according to step 1). Specifically:

[0047] If the fault is located in the ring network, multiple sags will occur and the voltage sag amplitude needs to be recalculated. If the fault is not located in the ring network, the voltage sag amplitude and duration at the sensitive load access point can be directly determined.

[0048] When the fault is located in the ring network, there is a time difference in the action time of the relay protection devices at both ends of the line. No matter which circuit breaker on both sides of the line is disconnected first, the network topology changes. In order to calculate the secondary sag amplitude after the single-end protection is tripped, the network impedance matrix needs to be corrected. After the protection is activated, it is equivalent to the line where the fault is located disappearing in the original topology, and an additional node a originally connected to the relay is generated. * The fault point is transferred from the original ab line to a in the new topology. * Based on the above equivalent dynamic transformation process, the node impedance matrix needs to be modified accordingly.

[0049] First, modify the elements of the original N-dimensional impedance matrix Z as follows to obtain Z1:

[0050]

[0051]

[0052]

[0053] Then add the additional node a in Z1 * The elements of one row and one column of , become (N+1)-dimensional matrix Z2, and the added elements are

[0054]

[0055]

[0056]

[0057] Finally, Z2 adds a row and a column of elements about the virtual fault node f, becoming an (N+2)-dimensional matrix Z3. The added elements are

[0058]

[0059]

[0060] After correcting the node impedance matrix, it is necessary to perform power flow calculation based on the new topology, update the pre-fault voltage of each node, and then bring it into the formula for calculation.

[0061] Furthermore, the comprehensive prediction model is specifically as follows: the exponential smoothing analysis model and the regression analysis model are used to generate respective prediction value data for the series data of the historical voltage sag duration of the distribution network, and the prediction values ​​are weighted and synthesized to obtain the final prediction data. Through step 3, it can be used to explore future development trends and obtain the predicted value of the relay protection action time of the final sensitive load access point line. It should be noted that the algorithm analysis mainly performs multi-dimensional correlation analysis and time series prediction on the historical data of the power grid relay protection. The reference value of the historical data is generally valid within the range of 5 to 10 years, otherwise it will lose its reference significance.

[0062] Specifically:

[0063] The exponential smoothing analysis model selects the weight value of each option as the average value of the decreasing exponential sequence, and eliminates the random fluctuations in the historical statistical sequence through a certain averaging method to find the main development trend. n , the first smoothing index formula is:

[0064] F t =αx t +(1-α)Ft-1 ;

[0065] Among them, α is the smoothing coefficient, 0<α<1, x t is the observed value (actual value) of the historical data sequence x at time t, F t and F t-1 is the exponential smoothing value (forecast value) at t and t-1.

[0066] The linear regression analysis model is suitable for prediction problems where the prediction object is mainly affected by a related variable and the two are linearly related. The mathematical equation of the linear regression model is Y=a+bX, which is used to analyze the linear relationship between the independent variable and the dependent variable.

[0067] The exponential smoothing analysis model and the regression analysis model are used to generate their respective predicted value data, and the predicted values ​​are weighted and synthesized to obtain the final predicted data. The comprehensive prediction model of the present invention uses linear combination prediction to determine the respective weights, i is the number of prediction model types, i = 1, 2, and the idea of ​​linear combination prediction is to select an appropriate weight k i Minimize the total error ε, the total error ε expression is as follows:

[0068]

[0069] in Combining the least squares method, the respective weights can be obtained as follows:

[0070]

[0071] Among them, ε i is the error of the i-th prediction model:

[0072]

[0073] Among them, F it is the predicted value of model i at time t, F 0t The actual value of the predicted object at time t.

[0074] Furthermore, the voltage sag amplitude, protection action time, and ITIC curve are combined to achieve the fixed value setting of the distribution network relay protection time, specifically:

[0075] 1) Obtain statistical data on voltage sag amplitude and protection action time at sensitive load access points.

[0076] 2) Combined with the ITIC curve, the voltage sag severity tolerance level of sensitive equipment is divided into three areas: tolerance area, equipment no damage area and equipment damage area. When the duration and amplitude of the voltage sag are in the equipment damage area (the upper part of the tolerance curve), once the equipment reaches this area, it will be damaged and the process will be interrupted; when the duration and amplitude of the voltage sag are in the equipment no damage area (the lower part of the tolerance curve), the operation process is normal in this case and the equipment itself will not be damaged; when the duration and amplitude of the voltage sag are in the tolerance area, the normal function of the equipment cannot be exerted, but it will not damage the equipment itself; therefore, using the equipment tolerance standard ITIC curve, the equipment tolerance is divided into A, AA, and AAA according to the duration and amplitude of the voltage sag event.

[0077] 3) Compare the voltage sag amplitude, protection action time data and ITIC curve parameter value, and optimize the protection setting value with the ITIC curve parameter value as the priority protection level. The specific steps are as follows:

[0078] If the voltage sag amplitude U sag And protection action time t sag When located in the equipment damage area, the tolerance of sensitive load equipment is classified as Class A. sag In this case, the first maximum time point in the equipment intact zone is used as the new setting protection time constant; among them, the equipment intact zone and the equipment damaged zone are in the voltage sag amplitude U sag The sag time at the intersection of the voltage and the equipment damage area is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the first maximum time point<the voltage sag amplitude U between the equipment intact area and the equipment damaged area sag The sag time at the intersection of Figure 3 In the case shown, the voltage sag at point A is 130% and lasts for 1 second. It is located in the equipment damage zone. The equipment will be damaged and the process will be interrupted. According to the ITIC curve, the protection time is set to the first maximum time point in the equipment non-damage zone, that is, time t.

[0079] If the voltage sag amplitude U sag And protection action time t sag When it is in the tolerance zone, the equipment tolerance is classified as Class AA. sag In this case, the second maximum time point in the equipment damage-free zone is used as the new setting protection time constant. sag The sag time at the intersection of the equipment non-destructive zone and the equipment tolerance zone is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the second maximum time point<the voltage sag amplitude U between the equipment non-destructive zone and the equipment tolerance zonesag The sag time at the intersection of Figure 4 In the case shown, the voltage sag at point AA is 40% and lasts for 0.1s, which is within the tolerance zone. The normal function of the equipment cannot be exerted. According to the ITIC curve, the protection time is set to the second maximum time point in the equipment non-destructive zone, that is, 0.01s.

[0080] If the voltage sag amplitude U sag And protection action time t sag When located in the equipment non-damage zone, the equipment's bearing capacity is classified as AAA and the initial set value is used.

[0081] According to another aspect of an embodiment of the present invention, a distribution network relay protection setting system considering the influence of voltage sag is provided, comprising:

[0082] An acquisition module is used to obtain the voltage sag amplitude at the access point of sensitive loads in the distribution network;

[0083] A judgment module is used to judge whether a multi-level sag occurs: if a multi-level sag occurs, the voltage sag amplitude of the sensitive load access point is recalculated;

[0084] A determination module, used to determine the line protection action time according to the comprehensive prediction model;

[0085] The execution module is used to set the relay protection time setting value of the distribution network according to the voltage sag amplitude, protection action time and ITIC curve.

[0086] By applying the above technical solution, it can be seen that the present invention can classify the voltage sag severity tolerance of sensitive equipment connected to the distribution network into different levels, adjust the protection action time for different levels of situations in combination with the ITIC curve, shorten the relay protection action time within the allowable range of the equipment, and minimize the impact of voltage sag on sensitive equipment.

[0087] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for setting relay protection values ​​of a distribution network considering the influence of voltage sag, characterized in that: include: Step 1, obtaining the voltage sag amplitude at the sensitive load access point of the distribution network; Step 2, determining whether a multi-level sag occurs: if a multi-level sag occurs, recalculating the voltage sag amplitude at the sensitive load access point; Step 3: Determine the line protection action time based on the comprehensive prediction model; Step 4: According to the voltage sag amplitude, protection action time, and ITIC curve, the relay protection time setting of the distribution network is realized; The voltage sag amplitude, protection action time, and ITIC curve are combined to realize the setting of the relay protection time of the distribution network, specifically: If the voltage sag amplitude U sag And protection action time t sag When located in the equipment damage area, the tolerance of sensitive load equipment is classified as Class A. sag In this case, the first maximum time point in the equipment non-destructive zone is used as the new setting protection time constant; If the voltage sag amplitude U sag And protection action time t sag When it is in the tolerance zone, the equipment tolerance is classified as Class AA. sag In this case, the second maximum time point in the equipment non-destructive zone is used as the new setting protection time constant; If the voltage sag amplitude U sag And protection action time t sag When located in the equipment non-damage zone, the equipment bearing capacity is classified as AAA and the initial setting value is adopted; The first maximum time point in the damage-free zone of the equipment is taken as follows: the voltage sag amplitude U sag The sag time at the intersection of the voltage and the equipment damage area is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the first maximum time point<the voltage sag amplitude U between the equipment intact area and the equipment damaged area sag The sag time at the intersection of The second maximum time point in the equipment lossless zone is taken as follows: the voltage sag amplitude U sag The sag time at the intersection of the equipment non-destructive zone and the equipment tolerance zone is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the second maximum time point<the voltage sag amplitude U between the equipment non-destructive zone and the equipment tolerance zone sag The sag time at the intersection of .

2. The method for setting the relay protection value of the distribution network considering the influence of voltage sag according to claim 1 is characterized in that: The step 2 is specifically: If multi-level voltage sag occurs, the distribution network topology will change, and the impedance matrix formed by the original distribution network structure needs to be corrected to recalculate the voltage sag amplitude, otherwise it will remain unchanged.

3. The method for setting the relay protection value of the distribution network considering the influence of voltage sag according to claim 1 is characterized in that: The comprehensive prediction model specifically comprises: using an exponential smoothing analysis model and a regression analysis model to generate respective prediction value data for the historical voltage sag duration series data of the distribution network, and performing weighted synthesis on the prediction values ​​to obtain final prediction data.

4. A distribution network relay protection setting value setting system considering the influence of voltage sag, characterized in that: include: An acquisition module is used to obtain the voltage sag amplitude at the access point of sensitive loads in the distribution network; A judgment module is used to judge whether a multi-level sag occurs: if a multi-level sag occurs, the voltage sag amplitude of the sensitive load access point is recalculated; A determination module, used to determine the line protection action time according to the comprehensive prediction model; The execution module is used to set the relay protection time value of the distribution network according to the voltage sag amplitude, protection action time, and ITIC curve; The voltage sag amplitude, protection action time, and ITIC curve are combined to realize the setting of the relay protection time of the distribution network, specifically: If the voltage sag amplitude U sag And protection action time t sag When located in the equipment damage area, the tolerance of sensitive load equipment is classified as Class A. sag In this case, the first maximum time point in the equipment non-destructive zone is used as the new setting protection time constant; If the voltage sag amplitude U sag And protection action time t sag When it is in the tolerance zone, the equipment tolerance is classified as Class AA. sag In this case, the second maximum time point in the equipment non-destructive zone is used as the new setting protection time constant; If the voltage sag amplitude U sag And protection action time t sag When located in the equipment non-damage zone, the equipment bearing capacity is classified as AAA and the initial setting value is adopted; The first maximum time point in the damage-free zone of the equipment is taken as follows: the voltage sag amplitude U sag The sag time at the intersection of the voltage and the equipment damage area is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the first maximum time point<the voltage sag amplitude U between the equipment intact area and the equipment damaged area sag The sag time at the intersection of The second maximum time point in the equipment lossless zone is taken as follows: the voltage sag amplitude U sag The sag time at the intersection of the equipment non-destructive zone and the equipment tolerance zone is the voltage sag amplitude U sag The sag time at the intersection of *10%≤the second maximum time point<the voltage sag amplitude U between the equipment non-destructive zone and the equipment tolerance zone sag The sag time at the intersection of .

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